Such a telecommunications network groups together a plurality of pieces of equipment, connections, and functions dedicated to transporting data coming from terminal equipment connected to the network. In particular, the transport functions may be implemented by activating routing and transmission protocols. A telecommunications network administered by an operator is also called a domain.
An IP connectivity service provider deploys a dedicated architecture to enable users of terminal equipment to be contacted. Access to the IP connectivity service is managed by the service provider using the telecommunications network of an operator to route data packets sent by pieces of terminal equipment to their final destination. Said service provider is sometimes also the operator of the telecommunications network.
The invention relates to a mechanism for allocating addresses and port numbers enabling the same primary address to be assigned to a plurality of pieces of terminal equipment of the telecommunications network.
Thus the invention applies to any type of public or private addressing, but it applies especially to public IP addresses defined by the Internet Protocol version 4 (IPv4), although this is not limiting on the invention.
In known manner, a home gateway between a terminal of a private home network and the public telecommunications network of an operator, also known as a domain, includes a table in which it associates the private IP address and the port associated with the terminal with an IPv4-type public IP address and a port of the same gateway on the public network.
This table is known to the person skilled in the art as a NAT (Network Address Translation) table.
It is commonly accepted in the IP service provider community that exhaustion of public IPv4 addresses is inevitable. To avoid this problem, the community has already taken action to define a new protocol, Internet Protocol version 6 (IPv6), which offers a large number of IP addresses and a hierarchical routing mechanism offering improved performance. However, that solution is not in practice activated by operators for financial or strategic reasons. The same providers are nevertheless not indifferent to recent warnings emanating from the Internet Engineering Task Force (IETF), especially in reports presented within the Global Routing Operations Working Group (GROW) concerning the risk of exhaustion of IANA IPv4 addresses by the end of 2009.
To limit the number of IPv4 public addresses necessary to provide an IP connectivity service, a dual NAT or Operator NAT solution has been proposed and implemented. It activates a NAT function in the telecommunications network of the operator so that the home gateways use private addressing in their NAT tables. Consider a piece of terminal equipment 120 in a home network RD connected to a home gateway 220 between the terminal equipment and a telecommunications network RT (see FIG. 1). The gateway implements a first NAT function NAT1 which translates a first private address pair of a data packet PT sent by the terminal equipment 120 into a second private address pair (PRIV2, P2). It then sends the transformed PT packet in the network RT. That packet is received by network equipment NO. This equipment NO executes an Operator NAT function NAT2 that translates the second private address pair (PRIV2, P2) of the data packet PT into a third public address pair (PUB3, P3). Thus it is the operator's NAT function that translates the private addresses of home gateways to public addresses, which saves a non-negligible number of IPv4 public addresses.
The Operator NAT solution has drawbacks, including:                the routing of IP data packets is made more complex: because of the introduction of a second level of address translation, data packets must be modified twice;        the need to adapt the implementation of conventional application or application level gateway (ALG) signaling protocols such as DNS (domain name system), FTP (file transfer protocol), or SIP (session initiation protocol). With the SIP, for example, in order to keep its NAT table up to date, setting up and maintaining a voice over IP session require the home gateway in the SIP signaling path to act, in known manner to force artificial exchanges of signaling between the subscriber's terminal and the public network, thereby imposing a high frequency of re-registration requests; in the presence of dual network address translation, such a mechanism must also be provided in the equipment that hosts the Operator NAT function;        degraded IP connectivity service offered by the operator of the public telecommunications network can only be deplored, especially because functions such as port forwarding or DynDNS cannot be supported in the presence of Operator NAT.        